1. Field of the Invention
The present invention is related to optical recording media, More specifically, the present invention is related to a thin-film optical recording medium and compatible materials that achieve high-density, high-resolution, high-speed recording of data, and are highly compatible with the full visible-light spectrum.
2. Description of the Related Art
Optical recording media has the advantage of easy recording and long-lasting data storage. Optical recording media is widely used in electronic publishing, multi-media data storage, and massive file-backup.
The structural components of conventional optical recording media include a substrate, a reactive layer, a reflecting layer and a protective layer, wherein the reactive layer is the primary recording element.
Typically, the reactive layer is made of organic dye. However, a reactive layer that is made of organic dye has disadvantages. First, organic dye can be easily degraded by environmental light exposure that results in a shortened product shelf life before recording. Second, the use of organic dye for optical recording media is less promising in future high-density optical-recording demands. Third, organic-dye formulation reacts within a narrow optical bandwidth and records with a specific wavelength of light source in a particular optical-recording system. Finally, production of organic dye requires organic solvents that might result in a certain level of environmental contamination.
Prior art (for example, JP Pat. No. 6-171236) discloses an inorganic optical recording medium with an Al/Au reflecting layer and a Ge reactive layer. The reflectivity of the design can be raised as high as 70%; however, the optical contrast after recording can only be elevated, not lowered, making it incompatible with the specifications of signal modulation of current optical recording media, and thus limiting its applications.
U.S. Pat. No. 5,458,941 discloses a reflecting layer consisting of Auxe2x80x94Cr, Auxe2x80x94Co, or Alxe2x80x94Ti and a reactive layer consisting of semiconductor materials. The reflecting layer is deposited on the incident side of the recording light beam to increase the reflectivity. However, this design requires higher recording power levels and thus limits its applications.
Recently, JP Pat. No. 08-274809 disclosed a recording layer consisting of a semiconductor layer and a reflecting metallic layer that can produce semiconductor/metal contacts inducing crystalline effect during light exposure. The amorphous semiconductor layer (the reacting layer, such as Si) will crystallize starting from the semiconductor/metal (such as Si/Al) interface which results in the modulation of the reflectivity of the recording layer. However, the signal modulation resulting from the amorphous/crystalline transformation is small and limited thereby limits the design""s applicability to the diverse specifications of optical recording media.
Indeed, neither the inorganic materials type nor the organic dye type optical recording media of the conventional art can fulfill future demands for a high-density recording within the full visible-light range.
The objective of the present invention is to provide a thin-film optical recording medium and compatible materials able to achieve high-density, high-resolution, high-speed recording of data. It is another object of the present invention to provide a thin-film optical recording medium and compatible materials highly compatible with the full visible-light spectrum.
To accomplish the above, the optical recording medium of the present invention is at least composed of a substrate, a transparent layer, and a reflecting layer. The present invention utilizes a light beam to heat the transparent layer and the reflecting layer, thereby forming a semi-transparent reflective area that is an alloy and/or compound of the transparent layer and the reflecting layer by means of an alloy/compound reaction. The alloy/compound reaction requires a minimum power-density threshold. The semi-transparent reflective area achieves the following effects: (1) reducing the effective thickness of the transparent layer and altering the respective optical path lengths, resulting in a shift of constructive or destructive interference patterns; and/or (2) transforming the optical constants (n and k) and thus the reflective intensity; and/or (3) altering the polarization angle. At least one of the above effects constitutes the mechanism that produces optical contrast before and after recording.
The thin-film optical medium and compatible materials disclosed in the present invention are therefore capable of (1) recording within the full visible-light range; (2) high-density recording; (3) high-speed recording; (4) high-definition recording; and (5) recording with a high degree of compatibility with diverse optical recording media formats.
The reasons are as follows: (1) The selected metal or alloys of the reflecting layer reflects light with sufficient intensity and can react with the selected materials of the transparent layer to create a semi-transparent reflective area at any wavelength within the full visible-light range such that an optimum optical contrast level can be achieved. Hence, the optical-recordable media of the present invention is suitable for a wide spectrum of recording light; (2) The reaction that generates the semi-transparent reflective area requires a distinctive threshold energy density, and only upper part of the laser beam (Gaussian distribution) is effective for forming the recording, resulting in much smaller recorded marks than the writing laser footprint, and therefore high-recording density can be achieved; and (3) Both atoms of reflecting layer and transparent layer diffuse only few hundreds of Angstroms to form the semi-transparent area, and this reaction is much faster than that in recording a dye-based recordable media or in recording a phase-change type rewritable media. Therefore, the optical disc in the present invention is suitable for high speed recording; (4) The reaction that generates the semi-transparent reflective area requires a distinctive threshold energy density, which results in a sharp and clear border for the semi-transparent reflective area and produces high-definition recording marks; (5) The recording power can be easily adjusted by selecting suitable materials for the reflecting layer, so that the optical recording medium of the present invention can accommodate recording-power requirements of various optical recording media.
Further, the thin-film optical medium and compatible materials of the present invention are capable of recording at a wide range of wavelengths and applicable to not only the CD systems or the developing DVD systems but also the future blue-light wavelength optical-recording systems. Furthermore, due to the minimum power density threshold requirement for the recording and the short time period of diffusion for the formation of recording mark, the recorded marks can be very small and quickly formed, making them superior for high-speed and high-density optical recording applications.
Another advantage of the present invention is that it provides a thin-film optical recording medium generating an optical reflective contrast that can be compliant with or counter to the current compact disk systems broadening the scope of its application. In addition, since the inorganic materials used in the present invention initiate reactions only above a threshold light intensity level, the thin-film design is insensitive to the general ambient lights and is therefore more optically stable and less apt to deteriorate compared to the dye-based recordable media.
Finally, the use of inorganic materials in the present invention eliminates the need for organic solvent(s), thus reducing environmental impact.